Various laser systems are discussed for use in dentistry today. The applicability of the Nd:YAG and the CO₂ laser is mainly limited by thermal side effects. No clinical indications are given for the UV-excimer lasers because of the low efficiency and the possible mutagenicity. The Er:YAG laser has an exceptional role. Because of his special thermomechanical process the Er:YAG laser can be used in many indications in dentistry today or in the future.

The analysis of mechanisms of hard dental tissues laser destruction is represented. The model describing thermal processes in human tooth under laser destruction is proposed. Numerically the optimum regimes of enamel and dentin processing is determined considering the minimum overheating of tooth pulp.

Absorption spectra of enamel, dentin, synthetic hydroxyapatite and deionized water were taken in the wavelength band 500 to 3000 nm. It could be shown that infrared radiation is mainly absorbed in the aqueous components of dental hard tissues. Because of their decreased water content extinctions measured are slightly lower than those of deionized water. Furthermore, mineral absorptions could be detected in the range of 2760 to 2840 nm with a maximum at 2800 nm in enamel and a smaller one at 2500 nm in dentin.

The object of this paper is to evaluate the thermal effect of the Er:YAG laser on human teeth and discuss the preliminary studies of the effects of water on the ablation efficiency of the Er:YAG laser. Human extracted teeth were sectioned into varying thicknesses in a horizontal plane and placed in a holder and aligned in a position where the laser was in focus on the surface of the tooth. First the laser was set at a known energy and the number of pulses needed to ablate through the known thickness of tooth were counted and a proportion of energy vs. ablation depth (etch rate) was determined. After etch rate was determined a thermocouple was placed on the back surface of the tooth section in line with the laser. The laser was then used to cut into the tooth just above the thermocouple and the temperature determined with and without water.

The ablative mechanism associated with the interaction of erbium:YAG laser radiation with dental tissue has been studied. The rates of ablation in dentine and enamel of extracted human teeth were determined and compared to a theoretical model. Ablative threshold energy densities were 10 +/- 2 and 25 +/- 8 J cm^-2 and effective absorption coefficients were 380 +/- 30 and 240 +/- 40 cm^-1, for dentine and enamel respectively. Using an optical probe beam, the dynamics of the ejected plume has been investigated in dentine. The mean velocity of the plume was 350 +/- 60 m s^-1. Histological sections of ablations were also produced, and the extent of secondary thermal damage assessed. The implications of these results for laser ablation of dental tissue are discussed.

The results of evaluation of Er:YAG radiation cavity preparation under transmitted and polarized light and by the electron microanalyzer are presented. We examined the longitudinal sections of intact teeth, teeth with early dental caries, teeth with laser preparation in enamel and teeth with Er:YAG laser preparation in enamel and dentine class I and V. We examined intact teeth and laser prepared teeth for the variation of mineralization. Phosphorus and calcium were regularly distributed. The margins of cavities had no necrosis zones. The defects of mineralization in caries depend on demineralization of hard tissues. In the structures was irregular loss of calcium and phosphorus. Thus, Er:YAG laser irradiation with water cooling has been found to be a non-invasive preparation technique.

We are presenting the results of the thermal changes of enamel, dentin and pulp temperature monitoring in extracted human teeth subjected to a pulsed Er:YAG laser radiation. We made a series of experiments irradiating the tooth using the pulsed Er:YAG laser and monitoring simultaneously the temperature of various parts of the tooth. The temperature was measured by the bead thermistor either in contact with the tooth surface or built in the pulp chamber. In the former experiments it was demonstrated, that the uncooled preparation can cause irreversible changes of the pulp. In the second part of the experiments the teeth have been cooled by flowing water. During the laser preparation of the enamel and the dentin the temperature did not increase more than 2 degree(s)C. In the moment of dentin perforation and hence laser irradiation of the pulp, the pulp temperature increased rapidly. The opening of the pulp coincides with the rapid temperature increase. These studies verified the feasibility of the pulsed Erbium:YAG laser use in stomatology.

Differing reports exist on the dependence of ablation rate in hard dental tissue on Er:YAG laser energy. In order to clarify this point we have carried out a systematic study of Er:YAG laser ablation rates in enamel and dentin extraorally with and without water spray cooling. Our findings confirm the existence of saturation of ablation rates at high laser energy densities which has been already previously attributed to plasma shielding. The drilling efficiency and the saturation effect have been found not to depend significantly on the presence of water spray. It is worth pointing out that a standard water spray, as used for mechanical drilling very efficiently eliminates any charcoaling, without reducing laser drilling efficiency. Diameters of ablated holes have been found to increase with laser energy also above the saturation of drilling efficiency. Measurements of the dependence of the ablation efficiency on pulse duration indicate that there is an optimal pulse duration for Er:YAG laser drilling of approximately 200 microsecond(s) .

Certain properties of the laser action on the hard tooth tissues have been studied, using free running pulsed Er-doped YAG, YSGG, YAP and YLF lasers, operating in 3 micrometers wavelength range. The influence of the laser radiation wavelength, power density and sample structure on the tooth destruction threshold have been studied.

Three different laser systems have been investigated according to their possible application in dentistry: a free running and a Q-switched microsecond Ho:YAG laser, a free running microsecond Er:YAG laser and picosecond Nd:YLF laser system consisting of an actively mode locked oscillator and a regenerative amplifier. The experiments focused on the question if lasers can support or maybe replace ordinary drilling machines. For this purpose several cavities were generated with the lasers mentioned above. Their depth and quality were judged by light and electron microscopy. The results of the experiments showed that the picosecond Nd:YLF laser system has advantages compared to other lasers regarding their application in dentistry.

The results of investigation of ultrashort Nd-laser pulses interaction with hard tooth tissues are represented. The values of laser radiation induced destruction thresholds and efficiencies of laser processing of enamel and dentin are measured. The results of observation of nonlinear optical effects of second harmonic generation and continuum generation in enamel and dentin below the damage thresholds are reported.

The purpose of this study was to examine the effects of root preparation with different laser types in order to replace hand-held instruments in periodontal surgery. The advantage should be a more selective and atraumatic technique promoting periodontal regeneration. The root surfaces of extracted human teeth were irradiated with pulsed laser radiation of IR lasers (CO₂, Ho:YAG and Tm:YAG laser) and excimer lasers (ArF* and XeCl* laser). For the light microscopic investigation the specimen were cut into undecalcified sections of 10 micrometers thickness and stained with Toluidine-blue.

First results of investigation of emission plume radiation stimulated by submillisecond YAG:Er, YAG:Cr,Tm,Ho and YAG:Nd pulsed laser radiation influence on hard tooth tissues are reported.

The results of experimental research of characteristics of acoustic waves generated under hard human tooth tissue destruction by YAG:Er and YAG:Cr,Tm,Ho laser submillisecond pulses are reported for the first time.

The application of the CO₂ laser continuous wave to hard dental tissue causes temperature changes on the impact area, on the adjacent area and inside the pulp chamber. The purpose of this study was to investigate the thermal effects induced by the CO₂ laser continuous wave, and the temperature flow through adjacent areas. Forty healthy molars, 15 molars with class II amalgam restoration and 10 canines with cervical caries extracted for periodontal reasons were irradiated with laser beam. On the occlusal surface the class I preparation was made just beyond the dentine-enamel junction. Temperature changes were measured at the enamel, root surface and at the cross section of the previously prepared holes 3 mm in diameter which were made 2 mm above the bifurcation level.

The pulsed photothermal radiometry of biological objects is used for controlling and investigation of tissue damage by YAG:Er ((lambda) equals 2,94 mkm), YAG:Nd ((lambda) equals 1,06 mkm), CO₂ ((lambda) equals 10,6 mkm) laser radiation thermal action, study of optical and thermophysical properties of tissue (tooth) in vivo.

Pre-ablative processes and destruction mechanisms of tissues under laser radiation are considered. It is shown that diffusion-limited processes of drying and carbonization may have a dramatic effect on the absorption and heating kinetics and on the change of laser ablation mechanisms. The manifestation conditions, advantages and disadvantages of various ablation mechanisms are discussed.

The treatment of 2989 patients with different type of lasers was described. The argon laser beam was used in 57 cases (portwine stains, telangiectasias, angiofibromas and other vascular lesions) and 84 operations were performed by Nd:YAG laser (leukoplakia, hemangioma etc.) furthermore 53 operations by combined laser beam. 2795 operations by carbon dioxide laser were performed in precancerous states and other white lesions, benign tumors and tumor-like states, malignant tumors and other lesions.

The vascular lesions of the oral cavity and face are frequently occurring lesions, their surgical treatment is often associated with various problems. The high energy CO₂, argon, Nd:YAG, Combi lasers ensures excellent results since its greatest advantage, i.e. the interincisive coagulation can be taken use of. Both of the patient and for the operating physician the laser surgery is superior to any other methods applied so-far. The experience obtained with the removal of 972 vascular lesions.

Dark colored stains, ranging from light blue to black, are disorders which often arise in the gums. Effective elimination of these melanotic disorders can be attempted by destroying the superficial layers of the gingiva. Treatment with monoline 514 nm green light (1.5 W, 300 ms, 0.5 mm spot size) produced by an Argon laser demonstrates, in clinical and histological controls, that due to good 514 nm light absorption by the pigment, elimination of the stains can be obtained and, in spite of the fact that the first layers of the tissue are destroyed, restoration of the mucosa status is optimal, giving excellent aesthetic results.

Carious regions of human teeth were investigated by means of remission-, fluorescence excitation- and fluorescence emission spectroscopy as well as time-resolved fluorescence measurements in the ns region. A detection of dental caries is possible with all of these spectroscopic methods. The peaks in measured remission- and fluorescence excitation spectra of carious regions correspond with the absorption bands of metal free porphyrins. The emission spectra and fluorescence decay kinetics indicate that protoporphyrin IX may be the main chromophore. HPLC measurement verify the existence of proto- (main component), copro- and probably Zn-protoporphyrin.

Our goal was to determine the fluorescence aided characterization of teeth. The incisors of 6 farmer pigs were opened with a round bur to expose the pulp. A Helium-Cadmium laser at a wavelength of 442 nm and operating at 17 mW was used as the excitation source. The light was guided through a 400 micrometers core diameter fiber which was used not only for delivery, but for the collection of tissue fluorescence. A spectrometer and an optical multichannel analyzer were used to detect and record the fluorescence signal.

Laser-Doppler flowmetry has been used for the assessment of pulp blood flow in health and disease. General purpose laser Doppler instruments working at the Helium-Neon (632,8 nm) as well as IR (750 - 810 nm) wavelengths have been used in this application. Specially designed handheld equipment has also been used to assess blood supply to the tooth. A considerable difference in the measurement results have been noticed when using different wavelengths and probe designs. In this study some of the problems related to the use of various wavelengths and probe designs are studied in human teeth and in a physical model of a tooth. Our results support the early observation that measurements at different wavelengths and with different probe designs cannot be directly compared.

The aim of this investigation was to improve the quality of the cured composite resin using the pulsed laser, thus avoiding disadvantages of previously used methods. The light source consisted of the pump excimer laser (Lambda Physik LPX 100) and the dye laser (Lambda Physik 3000). It is expected that pulsed laser polymerization could improve the conversion rate, decrease a temperature rise in the sample, allowing the `cooling' of the material and reduce polymerization shrinkage.